Paraguayan president Solano López ordered the imprisonment in response to the Brazilian invasion of Uruguay, before any formal declaration of war between Paraguay and the Empire of Brazil.

The capture of the Marquês de Olinda triggered events that led to the beginning of the Paraguayan War, although the true origin of the conflict is a reason for disagreement among historians.

[2] Its name was a tribute to prime minister, regent and president of the Imperial Council Pedro de Araújo Lima, the Marquis of Olinda.

[2] With the companies Bernal & Cárrega, first, and G. Matti & Cia, later, between 1860 and 1862, it carried out the route between the city of Buenos Aires and Corumbá under the command of Berrizo, with stops in San Nicolás de lós Arroyos, Rosario, Paraná, Corrientes and Asunción.

[1] At the time of the imprisonment, the Brazilian ship was commanded by the retired first lieutenant of the Imperial Navy Corps, Manoel Luiz da Silva Souto.

[5] From Rio de Janeiro to Cuiabá, sailing along the river, it took around 18 days; by land, although closer, it took months due to the many natural obstacles along the way.

Also, the Brazilian government had as a priority not to allow the Paraguayan union with the Argentine Confederation, which caused many problems due to its great political instability.

[5] This period of peaceful disagreement between Brazilians and Paraguayans ended with the death of president Carlos Antonio López; consequently, his son, Francisco Solano López, assumed the presidency and soon expanded the country's foreign policy, initiating talks with Argentine general Justo José de Urquiza, who governed the province of Entre Ríos,[5] and with the Blanco Party of Uruguay.

[11] Carreras, however, did not give up on getting some help from Solano López and, with the support of José Vasquez Sagastume, the Uruguayan minister residing in Asunción, tried to persuade him to take some hostile attitude, employing his army in actions that diverted Brazil's attention in Uruguay.

Sagastume also claimed that Paraguay had a powerful army, capable of launching a major offensive against Brazil to take many cities and territories, threatening to destroy the empire and leading emperor Pedro II to agree to peace terms that were convenient for him.

[12] He also stated that he was working to acquire these vessels, and that he would ask his country's Congress for authorization to take out a large loan in order to negotiate the acquisition of these ships in Europe.

[13] The Uruguayan government, impatient with Paraguay's delay in acting, sent several agents to that country on an unofficial mission to urge immediate action and inform whether López was really preparing for war.

On 9 November, the Brazilian steamer Marquês de Olinda was sailing on the Paraguay River, approaching the Fortress of Humaitá, on its regular voyage to the province of Mato Grosso.

On 11 November, Marquês de Olinda docked at the port of Asunción and began routine procedures, such as the rapid distribution of mail and the replacement of coal.

He had been informed, in a letter delivered that morning, that the Marquês de Olinda, escorted by the war frigate Amazonas, was transporting the new president of the province of Mato Grosso, along with a military engineer, and many weapons and a valuable cargo.

[16] It was around 6:30 am on 12 November, when Marquês de Olinda's crew spotted a column of smoke that was gradually increasing and which they soon identified as the Paraguayan steamer heading in towards them.

[15][17][18] After stopping Marquês de Olinda, a longboat from the Tacuarí took a letter to commander Manoel Luiz da Silva Souto ordering "the immediate return to Asunción and, in case of resistance, the captured ship be put under the fire of the corsair”.

On the 17th, a commission created by the Ministry of War and Navy of Paraguay, consisting of colonel Francisco Wisner de Morgenstern, José Falcón and another member of unregistered name, boarded the ship to examine the correspondence that the vessel was carrying, with the justification that they should know what was convenient for the Paraguayan public cause.

In fact, the commission searched the luggage of all crew members and passengers, even rummaging through the coal depot, which caused some animosity between a Brazilian officer and Falcón.

[21] Among the crew were the newly appointed president of the Mato Grosso province, Frederico Carneiro de Campos [pt] and a military engineer.

[24] In order to give an appearance of regularity to the capture of the Marquês de Olinda, an Admiralty Court was improvised to decide on the legality of the action.

All the steps taken, in the case of the capture of the Brazilian steamer, followed the direct orders of López and if any member of the court protested about the legality of the process, he would suffer consequences.

[25] On 30 August 1864, the Paraguayan government sent an ultimatum to the Empire of Brazil: “(...) the government of the Republic of Paraguay will consider any occupation of the Oriental Territory [Uruguay] by imperial forces... as an attack on the balance of the Platine States, which is of interest to the Republic of Paraguay as a guarantee of its security, peace and prosperity, and with the most solemn protest against such act, exempting itself from responsibility for events subsequent to the present declaration”.

The expedition was joined by the steamers Tacuarí, Paraguarí, Igurey, Río Blanco and Ypora; the schooners Independencia and Aquidabán, the patache Rosario and the boats Humaita and Cerro León.

[28] From then on, the largest interstate armed conflict in South America began, the Paraguayan War,[29] which would last for more than five years, until Solano López was killed in the Battle of Cerro Corá in 1870.

[33] Trying to help his companions, Marquês de Olinda approached the combat, but was prevented by Amazonas, which was previously firing at the coastal artillery batteries of José María Bruguez, who charged directly against the ship, ramming it and causing it to capsize, thus ending its participation in the war.